Elevator cable



Nav. 3, 1964 J. c. BURLEY 3,155,769

ELEvAToR CABLE Filed Sept. 29, 1960 INVENTOR. JOSEPH c. BURLEY ATTORNEYS United States Patent Oft-ice 3,155,769 ELEVATR CABLE loseph C. Burley, Milton, Mass., assigner to Boston Insulated Wire 7s Cable Co., Dorchester, Mass., a corporation of Massachusetts Filed Sept. 29, 1960, Ser. No. 59,267 6 Claims. (Qi. 174-121) This invention relates to elevator cables, land more particularly, to an elevator cable having `a novel and improved construction for controlling the bending stiffness of the cable.

luring the past 50 years, the design of elevators has generally centered around a relatively square cab type construction, with the cab having a nominal floor dimension or six by six feet. Elevator speed has generally varied between 50 feet per minute and 500 feet per minute. ln order to provide control of elevator operation from within the elevator, it is conventional to provide controls in the elevator connected to external controls by long ilexible cables. One end of such `an electrical power control cable is fixed in the elevator shaft while the other end of the cable is normally iixed to the bottom of the cab at the center portion thereof. The cable thus hangs in a loop with one leg of the loop being disposed between the cab and the wall of the elevator shaft or a next adjacent shaftway. It is of particular importance that an elevator control cable hangs in a loop configuration whereby the legs of the loop are substantially parallel to the elevator shaft. if such is not the case, the outer leg of the loop may swing inwardly of the shalt and strike the side of the cab `as it moves up and down; or the outer leg may swing outwardly against the side wall of the shaft or into a next adjacent shaftway where it may engage the cab therein.

it will thus be apparent that the exibility or degree of bending stillness of `an elevator cable must be closely controlled, as the degree of stillness controls the loop conguration of the cable, Where the cable is too flexible, the legs of the loop will hang in a generally V-shaped configuration and the outer leg will chate the cab causing ultimate failure of the cable. Where the cable is too rigid, the outer leg or" the loop may swing against the side wall of the shaft or into `an adjacent elevator shaft or there may be snarling or twisting of the cable. Thus, where the elevator cable is either too tlexible or too rigid, the cable will have an undesirably short service life.

ln recent years, the trend in elevator design has been to larger cabs having greater cab width to allow for wider opening doors and thus provide for quicker loading and unloading of passengers. Also, the trend has been to higher speeds of elevator operation; for example, up to 1000 feet per minute. With such high speed operation usually higher elevator shafts are involved so that the control cable is larger and its weight is increased proportionally. With such installations, in order to avoid excessive rocking of the cab during ascent or descent, it is particularly important that the cable be connected to the center of the cab floor and that the bight portion of the loop remains substantially stationary with respect to movement thereof laterally in the general plane of the loop. Further developments in elevators have been directed toward complete automation of the elevator operation. In such an installation, there is, of course, a substantial increase in the number of electrical control circuits on which the dependability, accuracy and precision of operation of the elevator depends. Accordingly, where previously perhaps 50 to 60 circuits were necessary in an elevator serving a twenty story building, modern elevators often require up to 250 circuits. This increase in the number of electrical circuits requires either the use of larger and thus heavier cables having an increased num- Patented Nov. 3, 1954 ber of conductors or the use of a proportionally larger number of the same size cable. The use of an increased number of small cables results in the possible entangling of the cables due to non-uniformity of motion between the cables and is, therefore, a hazard. Accordingly, it is preferable to provide for the increased number of circuits by utilizing larger cables having proportionally more conductors. Prior methods of controlling the bending stiffness of elevator cables are not, however, particularly suited to the larger cables as they result in undesirably high stresses in the conductors in the cables which -can cause permanent deformation or fracture of the conductors.

lt is an object of the present invention to provide an elevator cable having a novel and improved construction for controlling the bending stiffness of the cable.

lt is another object of the invention to provide a novel and improved elevator cable of the type described which will reduce the stresses normally present in the conductors of the cable during bending of the cable, thus increasing the service lite of the cable and materially reducing operational failures.

it is a further object of this invention to provide an elevator cable having a novel and improved construction whereby the degree of stiffness of the cable is controlled by means separate from the electrical conductors of the cable and in a manner so las to provide the desired loop configuration for each particular elevator design.

Other objects will be in part obvious, and in part pointed out more in detail hereinafter.

The invention accordingly consists in the features of construction, combination of elements and arrangement of parts which will be exemplified in the construction hereafter set forth and the scope of the application of which will be indicated in the appended claims.

In the drawing:

FlG. l is a diagrammatic elevational view of an exemplary elevator cab and shaft together with correct and incorrect elevator cable loop coniigurations;

FlG. 2 is a side elevational view ot an exemplary elevator cable embodying the present invention with the various components of the cable being partially removed to show the arrangement of components one within the other;

FlG. 3 is a diagnammatic view of a segment of one of the conductors of the cable of FIG. 2; and

FlG. 4 is a diagrammatic view of a segment of one of the conductors of the cable of FiG. 2 after bending of the cable.

With reference to FIG. l of the drawing, an exemplary elevator installation is shown as comprising a cab .i0 suspended in a sh Lt generally indicated at lil. An electrical power control cable i6 having an incorrect bending stiffness is shown in dotted lines. The lower end of the cable liti is connected to the center of the base of the cab while the upper end (not shown) of the cable is fixed in the elevator shaft. As can be seen from PEG. l, the cable 15 has excessive ilexibility= so that the bight portion t3 thereof is too narrow, and the outer leg 20 of the cable is inclined relative to the shaft axis so that it chates against the cab during movement of the cab. A cable 22 having the correct degree of stillness is shown in full line in FG. l. rShe cable 22 is installed in the same manner as the cable le but, as can be seen, it has a much wider bight portion 24. Further, the outer leg 26 of the cable hangs substantially parallel to the shaft axis so that during movement of the cab there will be no chafing of the cable against the cab. Rather, during movement of the cab the cable will have a substantially loop configuration, as shown in FlG. l, Ialthough the length of the bight portion 2d will, of course vary.

With reference to FIG. 2, an elevator electrical power control cable of the type with which this invention is conanotarse cerned generally comprises a center strength or structural member 3U) and a plurality of layers 32, 34, 36 and 38 of electrical conductors helically wound about the center member 30. Over the outermost layer 3S of electrical conductors is disposed a cotton braid 40. Over the cotton braid is wound a plurality of layers of tape 42. Over the tape is braided an outer sheath 44, which is usually impregnated with pitch or the like to provide a configuration generally as indicated at lo for the final appearance of the cable. ln the past, there have been various manufacturing practices and proposals for controlling the bending stiffness of an elevator cable of the general type shown in FIG. 2 so as to provide the desired loop configuration when the cable is installed in an elevator. For the most part, these efforts have been concerned with the lay angle of the helically wound electrical conductors in the various layers thereof, as well as with the tightness in which the components of the cable covering, and particularly the tapes 42 and sheath i4 are applied.

The effect of varying the lay angle of the conductors on the bending stiffness of the cable will be explained with reference to FIGS. 3 and 4. First, it should be stated, however, that for the purposes of this invention, and particularly the appended claims, lay angle will be defined as the angle that any particular component of the cable makes with a plane extending at right angles to the longitudinal axis of the cable. With reference to FIG. 3, there is diagrammatically shown an end view and layout of a portion of one of the helically wound conductors having a length corresponding to one complete revolution of the conductor about the cable axis. In the undeformed condition of the cable, this conductor portion will have a pair of sections disposed on opposite sides of a datum reference line extending diametrically of the cable. The length of both sections of the conductor portion will be L/Z,

where L is the total length of this portion of the conductor. However, when the cable is bent into a loop lying in a plane perpendicular to the plane of the drawing, and at right angles to the datum reference line, the length of the lower section of the conductor, on the outside of the loop, as shown in FIG. 4, will tend to increase in length by an increment X, while the length of the section of the conductor on the inside of the loop will tend to decrease in length by a corresponding amount. This change in length of the upper and lower halves of the conductor portion is caused by a tendency of the upper portion to creep circumferentially of the cable axis during bending of the cable. This creep of the conductor portion occurs during bending of the cable having helically wound conductors because of the tendency for the conductor section on the lower half of the cable to elongate inasmuch as it is in tension, while the conductor portion on the upper half of the cable is in compression and tends to shorten. Therefore, assuming that the conductors are not wound or bound too tightly so that the conductors are permitted at least limited relative movement to each other and the cable axis, the portion of the conductor on the inner side of the loop will, by the increment X, move circumferentially of the cable axis and downwardly to the underside of the loop as the cable is bent in the manner described. lt should be emphasized that the increment X refers to the increase in length of the conductor portion on the lower half of the cable, or outside half of the loop, which is due solely to circumferential movement ofthe conductor and not to elongation thereof due to excessive tension.

The amount of the increment X, or creep, is dependent upon the degree of bending of the cable, as well as upon the length L of the conductor portion with respect to the diameter of the helix in which it is wound and the extent of restriction of movement of the conductors. This latter factor corresponds to the lay angle of the conductor and the tightness with which the conductors are cabled. More specifically, the increment X is directly related to the degree of bending and the maximum increment X is Cit determined by the angle of lay and the amount of relative movement permitted between the conductor and cable axis. ln other words, the sharper the bending of the cable, the greater the tendency for the increment X to be larger. However, the greater the lay angle, the smaller the maximum increment X. Therefore, with a larger angle of lay, a lesser amount of bending is permitted before the maximum creep is reached. Thereafter, additional bending may cause excessive tension in the conductors and fracture thereof. This will be apparent if we consider a cable consisting of a plurality of layers of conductors, wherein each conductor extends parallel to the cable axis in radially spaced relation so as to provide a 9G degree angle of lay. In the bending of such a cable there is, of course, no movement of the conductors about the axis of the cable. Thus, it can be seen that if the angle of lay of the conductors is quite large, approaching 90 degrees, the conductors will contribute materially to the stiffness of the cable inasmuch as bending of the cable will result in a maximum degree of tension and compression on the conductors. However, it will also be apparent such a construction has the distinct disadvantage of placing unduly high stresses on the conductors tending to result in short service life due to early fatigue and fracture.

lt will also be observed that if the various layers of conductors are bound tightly upon each other and by the outer components of the cable, particularly the tape 42 and sheath 44, the movement of the conductors circumferentially about the cable axis during bending of the cable will be impeded. This will affect the bending stiffness of the cable. However, where the tape 42 and sheath Ml is wound or braided tightly over the conductors, the excessive friction between adjacent conductors in the same layer thereof, as well as between adjacent conductors in next adjacent layers will, during bending of the cable lo, tend to cause chafing of the insulation of the conductors with possible short circuiting between conductors. Further, if the tape and sheath is applied tightly it can, in effect, restrict, by binding, any circumferential movement of the conductors, so that during bending of the cable, the conductors are under either excessive compression or tension. As in the case of a straight conductor, this condition can result in early fatigue failure. Also, severe tension applied to the conductor can cause elongation of the conductor wire resulting in deformation thereof and an undesired loop configuration. It is the present standard practice in elevator cable construction to cable the conductors at a lay angle approaching degrees and to braid the sheath very tightly about the conductors so as to provide a hard compacted structure which will yield only slightly in a radially inward direction. As can be seen from the above, this provides a rigid cable, but at the expense of chang of the conductors and of undesirably high stresses in the conductors during bending of the cable. lt is also, perhaps, noteworthy, for a reason which will be later apparent, that the standard specification of elevator cables today is that the sheath liof the cable should be braided at a lay angle no greater than 45 degrees.

in accordance with the present invention, the conductors cf the layers 32, 34, 36 and 38 are cabled relatively loosely about the center member Sti at a predetermined lay angle which will provide a live center action for all normal bending of the cable. The covering lfor the conductors, namely, the braid all, 4tape 4,2-, and sheath (le are applied over the yconductors under relatively low tension, as compared to existing practices, so as not to adversely affect the live center action of the cable. As used herein, the term live center defines a center portion of a cable of the type described wherein during normal bending of the cable, `the conductors are not adversely impeded from circumferentially moving or creeping about the cable axis so that the conductors do not contribute a major part of the bending stiffness of the cable. This is achieved by cabling the conductors at lay angles such that during normal bending of the cable, the conductors will always be at a substantial angle to a cross sectional plane of the cable. Also included within this meaning of the definition of a live center, is a structure in which the conductors are not so tightly bound by the outer covering of the cable and that this circumferential movement of the conductors, during normal bending, is impeded to an adverse extent. Thus, With a live center, the conductors are never under maximum tension or compression during bending of the cable. Also, a live center will, as compared to existing elevator cable centers, be soft and readily yieldable or deformable radially inwardly of the cable axis. In a preferred ern- -bodiment of a cable constructed in accordance with this invention, the lay angle of the conductors in the various layers thereof is approximately 6568 degrees. While smaller lay angles might be used, this would result in 'shorter lays and thus, an increase in the length of conductor per unit length of cable with an attendant increase in the cost of the cable. The aforementioned angle of lay used in a particular embodiment was selected as the minimum .practical angle consistent with economy and performance.

In accordance with the invention, the cotton braid il is applied over the outer layer 3S of the conductors with a tension substantially less than that heretofore utilized and with a lay angle exceeding 45 degrees. In the specific embodiment shown, the primary purpose of the inner braid 40 is to provide a soft cushion between the outer layer 33 of the conductor and the subsequent outer covering layers of the cable. `Inasmuch as the lay angle of the braid 46 is greater than 45 degrees, the braid will tend to contribute some stiffness to the cable. However, the braid 4t? is rather loosely braided so that, during bending of the cable, substantial relative movement is permitted between the strands 38, land particularly those inclined in opposite directions. Also, the inner braid is dry, or in other words is not impregnated or otherwise treated with a material which might tend to restrict relative movement of the strands of the braid. Therefore, while the inner braid contributes to some extent to the stiffness of the cable, by reason of its large lay angle, it does not contribute a major portion of the cable stiffness.

In the specific embodiment shown, the tape 42. is applied in t-wo layers. The tape is applied under -a tension somewhat greater than that used when applying the braid 40. However, the tape is not applied with a tension suiiicient to compress the inner conductors and provide a hard center characterizing prior art cables. Rather the tape is applied with a tension which is low enough to preserve the live center characterizing feature of the cable of this invention. As can be seen in FIG. 2, the tape 42 comprises a layer 5@ of exible non-metallic threads woven into a square weave with the warp threads extending parallel to the longitudinal centerline of the tape and the weft threads extending at right angles to the longitudinal centerline of the tape. In the specific embodiment shown, the square woven inner layer of the `tape is in Contact with the braid 40 and is -fabricated from cotton so -as to offer relatively low resistance to relative movement between the strands of the braid 4t). The tape 42. is backed by a layer 52 of resilient yieldable material which, in the specific ernbodiment, is rubber. The rubber backing is adhered to the square woven inner layer of the tape and resists an; relative movement between the threads of the inner layer and particularly between the weft and wrap threads.

The tape is Wound over the braid 4d at a lay angle exceeding 45 degrees. In this manner, the warp threads of the square woven inner layer of the tape extend at a lay angle exceeding 45 degrees while the weft threads extend at a layer angle which is the complement of the layr angle of the warp threads. With a tape lay angle of greater than 45 degrees the corresponding lay angle of the warp threads of the tape will tend to result in an increase in stiffness of the cable. Further, `the tendency of the warp threads to move circumferentially about the cable 'axis is resisted by the rubber backing layer of the tape. Accordingly, the tape contributes to an increased bending stiffness of the cable, not by its being wound tightly upon the conductors so that it binds the same, but rather, by the lay angle 0f the Warp threads Vand the resistance to circumferential movement of the same, during bending of the cable. It is preferred that the lay angle of the tape be approximately the same as the lay angle of the inner braid 49. The weft threads of the tape will, 4of course, extend at a lay `angle of less than 45 degrees. However, the backing layer of the tape also tends to prevent circumferential movement yof the weft threads. Thus, the weft threads further tend to increase cable stiffness. The layers of tape also serve the purpose, as is conventional, of protecting the inner braid 4d from chang by the outer sheath 44.

The -outer sheath 44 comprises a plurality of strands 54 braided over the tape 42. Each strand comprises a plurality of iiexible, non-metallic parallel threads extending longitudinally of the strands. In accordance with the invention, the sheath 44 is braided about the tape under a tension somewhat greater than the tension used in winding the tape on the inner braid 4d. However, again, the tension applied to the strands S4 during braiding of the sheath 44 is insufficient to cause a compacting of the inner conductors which will adversely affect the live center action yachieved with a cable of this invention. In accordance with the invention, the sheath 44 constitutes the majority -of the stiffness to the cable in a Amanner which does not result in a compacted hard center as in prior cables. Specifically, the strands of the sheath 44 are braided at `a lay angle greater than 45 degrees so that during normal bending of the `cable the strands of the sheath on the under side of the loop will have a decreased tendency to creep about the cable axis. Preferably, the lay angle of the `strands 54 is approximately equal to the lay angle of the inner braid 4d. Further, the sheath is impregnated with a suitable resilient yieldable material, such as asphalt, rubber lor plastic, which further tends to prevent any relative movement between next adjacent strands and particularly between next adjacent overlying strands inclined in opposite directions. The resilient yieldable material contacting the strands 54, and threads making up the strands, will thus yfurther tend to prevent circumferential movement of the strands, to `further increase the tension in the strands during bending of the cable and thus further increase the bending stiffness of the cable.

Accordingly, it can be seen that there has been provided a novel and improved elevator cable having a live center portion in that the cable conductors are relatively free to move circumferentially about the cable axis during normal bending of the cable, thus, materially reducing chafing between conductors `and a substantial reduction in tension and compression stresses on the conductors during cable bending so as to materially increase the service life of the conductors. Contrary to prior art practices, the desired bending stiffness for the cable is provided by means separate from the conductors. The stiffness imparted to the cable is a result of the construction and `arrangement of the inner braid 40, tape 42 and sheath 44 and not by the tight winding of these elements around the conductors as heretofore practiced. By the proper selection of the lay angle of the strands 54 of the sheath,

the stiffness of the cable may be varied to provide the desired loop configuration for any size cable. The stiffness provided by the sheath of the cable is directly related to the lay angle of the strands 54 which, as noted above, is greater than 45 degrees, again contrary to presently established standards and practices.

While this invention has been described in terms of the specific embodiment shown in the drawing, it will be understood that the invention is not limited `to this specific structure for an elevator cable. As will be apparent to those skilled in the art, the invention resides in the controlling of the stiffness of an elevator cable by the provision of flexible non-metallic stiifening members separate from the conductors, such as the strands of ,the sheath, or threads of the inner braid and tape, which have a lay angle of greater than 45 degrees and which are contacted by a resilient yieldable material which tends to prevent circumferential movement of the stiiiening members. Thus, elevator cables having structures different from that of the specific embodiment shown, could be provided without departing from the scope of this invention. For example, while the sheath ofthe cable has been illustrated as an impregnated braided structure, it could be in the form of a rubber or plastic tube in which is embedded a plurality of non-metallic stitlening members or threads having lay angles greater than 45 degrees. Such `a structure would satisfy the requirements of the invention regarding lay angle and of contacting the stiifening members with a resilient yieldable material so `as to tend to prevent circumferential movement of the stitfening members about the cable axis during bending of the cable. Accordingly, it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

It is also to be understood that the language in the following claims is intended to cover all of the generic and speciic features of the invention herein described and all statements of the scope of the invention which, as a matter of language, might be said to fall therebetween.

l claim:

1. In an elevator electrical power control cable, a live center portion including a plurality of cabled insulated electrical conductors, means separate from said center portion to provide the cable with a predetermined bending stiffness greater than the bending stiffness of said center portion alone and comprising an outer cable sheath, said sheath including a plurality of flexible non-metallic members braided about the conductors at a predetermined lay angle greater than 45 degrees, said sheath being impregnated with yieldable resilient material tending to prevent relative movement between said members during bending of the cable.

2. ln an elevator electrical power control cable, a flexible center portion including a plurality of electrical conductors, means separate from said center portion to control the bending stiiness of the cable comprising an outer sheath for the conductors, said sheath including a plurality of flexible non-metallic members braided about the conductors, said sheath being impregnated with ak yieldable resilient material tending to prevent relative movement between next adjacent strands during bending of the cable, and flexible tape wound about the conductors and disposed between the conductors and sheath, said tape comprising a layer of square woven non-metallic materialbacked by a layer of exible resilient material adhered to Said square woven material, said tape having a lay angle exceeding 45 degrees.

3. An elevator electrical power control cable comprising, a live center portion including a plurality of layers of cabled electrical conductors, a quantity of exible nonmetallic tape wound over the conductors and covering the same, and a braided non-metallic sheath covering the tape, s-aid sheath and tape providing the majority of the bending stiness of the cable and each including a plurality of flexible non-metallic strands, and resilient yieldable material contacting the strands of each of the tape and sheath and tending to prevent relative movement therebetween during bending of the cable.

4. An elevator electrical power control cable comprising, a live center portion including a plurality of layers of cabled electrical conductors, a quantity of flexible nonmetallic tape wound over the conductors and covering the same, and a braided sheath covering the tape, said sheath and tape each including a plurality of strands applied at a predetermined lay angle greater than 45 degrees and yieldable resilient material acting on the strands of each of the tape and sheath and tending to prevent relative movement between the strands of each during bending of the cable.

5. An elevator electrical power control cable comprising, a live center portion including a plurality of cabled electrical conductors, an inner dry braid including a plurality oi strands of iiexible non-metallic material braided over the conductors and having a lay angle exceeding 45 degrees, a quantity of tape wound over said inner braid, said tape including an inner layer or" square woven ilexible non-metallic material facing the inner braid and backed by a layer of resilient yieldable material adhered to the inner layer and resisting relative movement between the square woven lthreads of the inner layer, the tape being applied over the inner braid so that the warp threads of the inner layer have a lay angle exceeding 45 degrees, and a sheath surrounding the tape and including a plurality of non-metallic flexible strands braided over [the tape and impregnated with a resilient yieldable material.

6. An elevator electrical power control cable comprising, a flexible l-ive center portion which is readily deformable in a direction radially inwardly of the cable axis and which includes a plurality of layers of cabled electrical conductors, and means separate from said ccn- 'ter portion controlling the stiffness of the cable and comprising a dry cotton braid surrounding said live center portion, at least one layer of tape wound over the braid tighter than said inner braid is braided over the conductors, said tape including an inner layer of square woven non-metallic material facing said braid and a backing layer of rubber-like material adhered to said inner layer and resisting relative movement between the threads of said inner layer, and a sheath applied over the tape, said sheath including a plurality of flexible non-metallic strands braided over the tape at a lay angle greater than 45 degrees, said sheath being braided over said tape tighter than the tape is wound on the inner braid, said sheath being impregnated subsequent to braiding thereof with a resilient yieldable material tending to resist movement between said strands during bending of the cable.

Reierences Cited in the file of this patent UNITED STATES PATENTS 513,982 Chick Feb. 6, 1894 2,212,360 Aken Aug. 20, 1940 2,759,990 Bean Aug. 2l, 1956 FORElGN PATENTS 577,i52 Great Britain May 7, 1946 

1. IN AN ELEVATOR ELECTRICAL POWER CONTROL CABLE, A LIVE CENTER PORTION INCLUDING A PLURALITY OF CABLED INSULATED ELECTRICAL CONDUCTORS, MEANS SEPARATE FROM SAID CENTER PORTION TO PROVIDE THE CABLE WITH A PREDETERMINED BENDING STIFFNESS GREATER THAN THE BENDING STIFFNESS OF SAID CENTER PORTION ALONE AND COMPRISING AN OUTER CABLE SHEATH, SAID SHEATH INCLUDING A PLURALITY OF FLEXIBLE NON-METALLIC MEMBERS BRAIDED ABOUT THE CONDUCTORS AT A PREDETERMINED LAY ANGLE GREATER THAN 45 DEGREES, SAID SHEATH BEING IMPREGNATED WITH YIELDABLE RESILIENT MATERIAL TENDING TO PREVENT RELATIVE MOVEMENT BETWEEN SAID MEMBERS DURING BENDING OF THE CABLE. 